In most vehicles, ambient air temperature (AAT) sensors are employed to measure and display the outside air temperature to a vehicle operator. The measured air temperature is often utilized in engine controls and on-board diagnostics procedures. For example, fuel system leak test diagnostics may base test pass/fail thresholds at least partially upon the measured AAT. As another example, an engine controller may determine how much to enrich the air-to-fuel ratio based on the measured AAT. The AAT is often inferred and/or estimated by way of under hood temperature sensors. However, the measured AAT by AAT sensors can be inflated due to excessive radiant heat transferred to the AAT sensor from the engine, sun load, road surface, and the like. Similarly, the measured AAT by AAT sensors may be depressed due to snow or rain contacting the surface or the AAT sensor, and evaporative cooling of the contacting precipitation. Erroneous AAT measurements input to OBD and engine controls can reduce vehicle drivability, increase fuel consumption, and increase fuel emissions. Furthermore, displaying excessively inflated AAT at a vehicle instrument panel can be disconcerting to a vehicle operator.
One example approach of diagnosing a faulty temperature sensor is shown by Hamama et al. in U.S. Pat. No. 8,608,374. Therein, an outside air temperature (OAT) diagnostic system includes an ambient temperature monitoring module that receives an OAT signal from an OAT sensor and an intake air temperature (IAT) signal from an IAT sensor of an engine. The ambient temperature monitoring module compares the OAT signal to an IAT signal and generates a first difference signal. A performance reporting module determines whether the OAT sensor is exhibiting a fault and generates an OAT performance signal based on the first difference signal. Other attempts to address faulty vehicle ambient temperature sensors include Martin et al. U.S. Pat. No. 9,114,796. Therein, an engine temperature is compared to each of an intake air temperature sensed before an engine start but after sufficient engine soak, as well as an intake air temperature sensed after selected vehicle operating conditions have elapsed since the engine start. Based on discrepancies between the air temperature and the engine temperature, degradation of the sensor is determined.
The inventors herein have recognized potential issues with such systems. As one example, the above-mentioned approaches fail to detect erroneous ambient temperature measurements caused by excessive radiant heat transferred to the AAT sensor from solar load, the engine, the road surface, and the like. Similarly, the above-mentioned approaches fail to detect erroneous ambient temperature measurements caused by precipitation of snow or rain contacting the AAT sensor and evaporative cooling of the contacting precipitation. Furthermore, a method for reducing the radiant heat transferred to the AAT sensor, reducing precipitation from contacting the AAT sensor, and for correcting the inflated or depressed AAT sensor measurements is not provided. As such, radiant heat loads at the AAT sensor may result in a false indication of a faulty AAT sensor.
In one example, the issues described above may be at least partially addressed by a method for a vehicle including an ambient air temperature (AAT) sensor, the method comprising, in response to an AAT measured by the AAT sensor deviating from an expected AAT by more than a threshold temperature difference, adjusting a vehicle actuator to reduce the deviation of the AAT measured by the AAT sensor from the expected AAT, and remeasuring the AAT with the AAT sensor after adjusting the vehicle actuator. In this way, radiant heat loads at the AAT sensor can be reduced, depressed AAT measurements at the AAT sensor can be reduced, and inflated or depressed AAT measurements by the AAT sensor can be corrected, thereby increasing an accuracy of the AAT sensor measurements, and reducing a risk of misidentifying a faulty AAT sensor. As one example, the remeasured AAT may deviate from the expected AAT by less than the threshold temperature difference because adjusting the vehicle actuator aids in insulating the AAT sensor from the radiant heat load or from a cooling source such as precipitation. As such, the integrity of OBD and engine control methods can be maintained, thereby reducing or maintaining fuel consumption, fuel emissions, and vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.